The present invention relates to an ultrasound liquid atomization system capable of atomizing liquids, mixing liquids, and/or separating liquids from gases, liquids, solids, or any combination thereof suspended and/or dissolved within a liquid.
Liquid atomization is the process by which a quantity of liquid is broken apart into small droplets, also referred to as particles. Liquid atomizers have been utilized in a variety of applications. For instance, liquid atomizers have been utilized to apply various coatings to devices. Gasoline is injected into most modern engines by use of a liquid atomizer, often referred to as a fuel injector. Delivering therapeutic substances to the body as to treat asthma or wounds is often accomplished through the use of liquid atomizers.
Traditional liquid atomizers, such as those generally employed as fuel injectors, utilize pressure to disperse a liquid into smaller droplets. These injectors function by forcing a pressurized liquid through small orifices opening into a larger area. As the liquid passes from the small orifice into the larger area, the atomized liquid-increases in volume.
Conceptually, this is similar to the inflation of a balloon and can be represented by the equation:
  Volume  =                    (                              A            ⁢                                                  ⁢            constant                    ,          k                )            ×              (                  Area          ⁢                                          ⁢          outside          ⁢                                          ⁢          the          ⁢                                          ⁢          orifice                )                    (              Force        ⁢                                  ⁢        pushing        ⁢                                  ⁢        the        ⁢                                  ⁢        liquid        ⁢                                  ⁢        through        ⁢                                  ⁢        the        ⁢                                  ⁢        orifice            )      
According to the above equation, as the area into which a liquid is forced gets larger the volume of the liquid begins to increase. Thus as the liquid initially exits from the small orifice of a typical fuel injector, the liquid forms an expanding drop very similar to an inflating balloon. The liquid exiting from the injector is initially retained in the drop by the surface tension of the liquid on the surface of the drop, which is conceptually similar to the elastic of a balloon. Surface tension is created by the attraction between the molecules of the liquid located at the surface of the drop. As the volume of the liquid increases, the drop at the injector's orifice begins to expand. Expansion of the drop moves the molecules at the surface of the drop farther away from each other. Eventually, the molecules on the surface of the drop move far enough away from each other as to break the attractive forces holding the molecules together. When the attractive forces between the molecules are broken, the drop explodes like an over inflated balloon. Explosion of the drop releases several smaller droplets, thereby producing an atomized spray.
Atomized sprays can also be generated through the use of ultrasonic devices. These devices atomize liquids by exposing the liquid to be atomized to ultrasound, as to create ultrasonic vibrations within the liquid. The vibrations within the liquid cause molecules on the surface of the liquid to move about, disrupting the surface tension of the liquid. Disruption of the liquid's surface tension creates areas on the surface of the liquid with reduced or no surface tension, which are very similar to holes in a sieve, through which droplets of the liquid can escape. Devices utilizing this phenomenon to create a fog or mist are described in U.S. Pat. No. 7,017,282, U.S. Pat. No. 6,402,046, U.S. Pat. No. 6,237,525, and U.S. Pat. No. 5,922,247.
Disrupting the surface tension of a liquid with ultrasonic vibrations can also be utilized to expel a liquid through small orifices through which the liquid would not otherwise flow. In such devices the surface tension of the liquid holds the liquid back, like a dam, preventing it from flowing through the small channels. Exposing the liquid to ultrasound causes the liquid's molecules to vibrate, thereby disrupting the surface tension dam and allowing the liquid to flow through the orifice. This phenomenon is employed in inkjet print cartilages and the devices described in U.S. Pat. No. 7,086,617, U.S. Pat. No. 6,811,805, U.S. Pat. No. 6,845,759, U.S. Pat. No. 6,739,520, U.S. Pat. No. 6,530,370, and U.S. Pat. No. 5,996,903.
Ultrasonic vibrations have also been utilized to enhance liquid atomization in pressure atomizers such as fuel injectors. Again, the introduction of ultrasonic vibrations disrupts or weakens the surface tension holding the liquid together, making the liquid easier to atomize. Thus, exposing the liquid to ultrasonic vibrations as the liquid exits a pressure atomizer reduces the amount of pressure needed to atomize the liquid and/or allows for the use of a larger orifice. Injection devices utilizing ultrasound in this manner are described in U.S. Pat. No. 6,543,700, U.S. Pat. No. 6,053,424, U.S. Pat. No. 5,868,153, and U.S. Pat. No. 5,803,106.
Atomizers relying on pressure, in whole or in part, to atomize liquids are sensitive to pressure changes in the environment into which the atomized liquid is to be injected. If the pressure of the environment increases, the effective pressure driving liquid atomization decreases. The decrease in the effective pressure driving and/or assisting liquid atomization occurs because the pressure within the environment pushes against the liquid as the liquid exits the atomizer, thereby hindering atomization and expulsion from the atomizer. Conversely, if the pressure of the environment into which the atomized liquid Is injected decreases, the effective pressure driving and/or assisting liquid atomization increases.
Ultrasonic waves traveling through a solid member, such as a rod, can also be utilized to atomize a liquid and propel the atomized liquid away from the member. Such devices function by dripping or otherwise placing the liquid to be atomized on the rod as ultrasonic waves travel through the rod. Clinging to the rod, the liquid is transported to the end of the rod by the ultrasonic vibrations within the rod. An everyday example of this phenomenon is a person attempting to pour water from a glass by holding the glass at a slight angle. Instead of the water pouring put of the glass and dropping straight down to the floor, the water clings to and runs along the external sides of the glass before falling from the glass to the floor. Similarly, the liquid to be atomized clings to the sides of an ultrasonically vibrating rod as the liquid is carried towards the end of the rod by ultrasonic waves traveling through the rod. Ultrasonic wave emanating from the tip of rod atomize and propel the liquid forward, away from the tip. Devices utilizing ultrasonic waves to atomize liquids in such a manner are described in U.S. Pat. No. 6,761,729, U.S. Pat. No. 6,706,337, U.S. Pat. No. 8,663,554, U.S. Pat. No. 8,589,099, U.S. Pat. No. 6,247,525, U.S. Pat. No. 5,970,974, U.S. Pat. No. 5,179,923, U.S. Pat. No. 5,119,775, and U.S. Pat. No. 5,076,268.
In such devices, care must be utilized when delivering the liquid to the vibrating rod. For instance, if the liquid is dropped from to high of a point a majority of the liquid will bounce off the rod. The devices depicted in U.S. Pat. No. 5,582,348, U.S. Pat. No. 5,540,384, and U.S. Pat. No. 5,409,163 utilize a meniscus to gently deliver liquid to a vibrating rod. The meniscus holds the liquid to be atomized between the vibrating rod and the point of delivery by the attraction of the liquid to the rod and the point of delivery. As described in U.S. Pat. No. 5,540,384 to Erickson at al., creation of a meniscus requires careful construction and design of the liquid delivery point. Furthermore, if the delivery pressure of the liquid changes, the meniscus may be lost. For instance, if the delivery pressure suddenly increases, the liquid may become atomized before a meniscus can be formed. Destruction of the meniscus may also occur if the pressure outside the liquid delivery point suddenly changes. Thus, use of a meniscus to deliver a liquid to be atomized to a vibrating rod is generally limited to situations where the construction of the device, the design of the device, and the environment in which the device is used can be carefully monitored and controlled.
According there is a need for a liquid atomization system that enables the production and release of a consistent spray of an atomized liquid into an environment, despite changes in the pressure of the environment into which the atomized spray is injected.